2000AJ....119..901S

The orbital period of two Algol-type binaries, RW CrB and TU Her, are studied. It is discovered that the orbital period of RW CrB shows a secular decrease at the rate of dP/dt=-4.29x10^–8 days.yr^–1, while the orbital period of TU Her varies in some complex way. Two jumps in the orbital period are found while it undergoes secular decrease at a rate of dP/dt=-2.92x10^–6 days.yr^–1. The rates of decrease of the orbital periods dP/dt in other Algol-type binaries are revised and the statistical relation between the orbital period P and its rate of change dP/dt is also discussed. The properties of the changes in the orbital period of these systems, combined with their semidetached configurations, demonstrate that they may be undergoing secular mass and angular momentum loss (AML) during their evolution. The irregular abrupt changes that are superposed on the secular decrease of the orbital period may be caused by some instabilities during the mass transfer and AML.